Environmentalists might think they’ve scored an unlikely ally in Roger Scruton, arguably Britain’s most famous philosopher—and a proud conservative. But Mr. Scruton’s case for environmentalism is classically conservative, centered on the love of home, the importance of local institutions, and especially the suspicion of state power.

With “How to Think Seriously About the Planet” (out next month in the U.S.), Mr. Scruton casts his lot with environmentalism but not with the contemporary environmentalist movement. The book is something of a cry in the wilderness, keeping wary distance from all sides of the current political debate. “It’s an attempt,” as he puts it, “to say, ‘Look, wake up, here is what it’s all about really.’”

On a radiant spring afternoon, I have tea with Mr. Scruton at his farmhouse in the Cotswolds. Over more than four decades, he has written tracts on Spinoza and Kant, among other heavyweight subjects from sexual desire to music and hunting. But Mr. Scruton seems most at home fighting to defend traditional culture against its despoilers: fragmentation, nihilism, disenchantment, postmodernism.

Dressed in a rumpled sweater and corduroy trousers, his craggy face crowned by an unruly thicket of dust-colored hair, Mr. Scruton certainly looks the part of weathered back-country scholar. Lush hills spill in all directions outside the windows in his living room, where the 68-year-old is settled into an easy chair. The culture warrior is in his element.

Not that Mr. Scruton, ever the anti-radical, would describe what he wages from his desk in rural Wiltshire as “warfare.” His practice is to tear through liberal convictions without abandoning his calm erudition.

On immigration policy: “The real cure to immigration, obviously, is to make sure that there is prosperity around the world so that people don’t have the motive. Not just prosperity, but freedom.”